1. Field of the Invention
The present invention relates to a biaxially stretched polyester film for protecting a back surface of a solar cell, and a method for producing a polyester resin. More specifically, the invention relates to a biaxially stretched polyester film for protecting a back surface of a solar cell, the polyester film being improved in hydrolysis resistance and electrostatic adhesion property, and a method for producing a polyester resin.
2. Background Art
A polyethylene terephthalate resin is used as a material of a back surface sealing film of a solar cell, which is one of constitutional members of a solar cell. A solar cell is used outdoors, and thus a back surface sealing film of a solar cell is strongly demanded to have resistance to the natural environments (i.e., hydrolysis resistance).
Separately, associated with the demand of increasing the film forming speed in recent years, there is a demand of a polyethylene terephthalate resin having a low volume resistivity that is produced by an electrostatic film casting method, which has been ordinarily used, for further enhancing the film forming speed.
For addressing the demands, techniques for achieving the high-speed film formation and the hydrolysis resistance simultaneously have been proposed by determining the kinds and the mixing ratios of the catalyst and the additives to specific ranges in the melt polymerization process of a polyester resin (see, for example, PTLs 1 and 2).